package com.lin.chapter27;

import java.util.Map;
import java.util.Stack;

public class Calculator {
	private Expression expression;

	public Calculator(String expStr){
		Stack<Expression> stack = new Stack<>();
		char[] charArray = expStr.toCharArray();

		Expression left;
		Expression right;
		for (int i = 0; i < charArray.length; i++) {
			switch (charArray[i]){
				case '+':
					left = stack.pop();
					right = new VarExpression(String.valueOf(charArray[++i]));
					stack.push(new AddExpression(left, right));
					break;
				case '-':
					left = stack.pop();
					right = new VarExpression(String.valueOf(charArray[++i]));
					stack.push(new SubExpression(left, right));
					break;
				default:
					stack.push(new VarExpression(String.valueOf(charArray[i])));
			}
		}
		this.expression = stack.pop();
	}

	public int run(Map<String, Integer> var){
		return this.expression.interpreter(var);
	}
}
